US Airways Inc. and American Airlines Inc. are demanding the names of people that Justice Department attorneys interviewed before filing a lawsuit to block a merger of the two carriers.

A motion filed Tuesday in U.S. District Court in Washington, D.C., seems to be an attempt to see if the airlines can find the fingerprints of any other airline’s employees — or anyone else — on the department’s decision to file the antitrust lawsuit.

“Plaintiffs investigated the challenged merger for many months before filing suit, interviewing third parties and gathering information they believe justifies their attempt to block the merger,” the carriers said in their motion.

They said they previously filed an interrogatory — a written set of questions — with the Justice Department in which they asked for “the identities of the third parties who plaintiffs interviewed and the factual information those witnesses disclosed.”

However, the airlines said Justice officials were “eager to hold back the information they learned.” The department declined the airlines’ request for information Thursday.

In its response, the department said the information sought was “protected from discovery and disclosure by the attorney-client privilege, deliberative-process privilege, work product doctrine, law enforcement investigative privilege, common-interest privilege or any other applicable privilege or doctrine.”

“Not so,” the airlines argued. They said they were seeking “only routine pretrial discovery of facts.”

The motion and response are part of the pretrial sparring that began soon after the department and a number of state attorneys general filed the lawsuit Aug. 13. The suit contends the merger would be anti-competitive and would hurt consumers.

The two sides have already fought out their differences on a trial date. The carriers wanted a Nov. 12 trial, while the government wanted to hold it next March. U.S. District Judge Colleen Kollar-Kotelly eventually decided to start the trial Nov. 25.

In a motion last week, the two airlines also asked for all the information that Justice attorneys used when the government “cleared” four previous airline mergers between 2005 and 2011.

In response, the department said it objected “generally to the term ‘previously cleared mergers’ to the extent it assumes that any of the plaintiffs ‘cleared’ the four consummated mergers listed.”

The information sought “is neither relevant to the subject matter of the lawsuit nor reasonably calculated to lead to the discovery of admissible evidence,” the department said in its response Thursday.

The “exercise of prosecutorial discretion in prior investigations,” the DOJ stated, “bears no relevance to the question of whether the merger between US Airways and American substantially lessens competition.”

The issues on discovery and interrogatories will go to special master Richard A. Levie, appointed in early September to resolve disputes on those matters.

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